• How kubernetes hides away the volumeMounts complexity

    4 min read

    volumeMounts overlay kubernetes

    If we try compare volumeMounts with the actual mounts that we have on a pod using, for example, df it can be quite confusing due to the usage of the overlay filesystem

    Let's consider the volumeMounts section of a deploy:

    $ kubectl get deploy pet2cattle -o yaml
(...)
          volumeMounts:
          - mountPath: /opt/pet2cattle/conf
            name: config
          - mountPath: /opt/pet2cattle/data
            name: pet2cattle
            subPath: data
          - mountPath: /opt/pet2cattle/lib
            name: pet2cattle
            subPath: lib
          - mountPath: /tmp
            name: tmp-dir
(...)

    And compare it with the filesystem we see on the pod:

    $ kubectl exec pet2cattle-8475d6697-jbmsm -- df -hP
Filesystem      Size  Used Avail Use% Mounted on
overlay         100G  9.7G   91G  10% /
tmpfs            64M     0   64M   0% /dev
tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/xvda1      100G  9.7G   91G  10% /tmp
shm              64M     0   64M   0% /dev/shm
/dev/xvdcu       20G  2.5G   18G  13% /opt/pet2cattle/lib
tmpfs           3.9G   12K  3.9G   1% /run/secrets/kubernetes.io/serviceaccount
tmpfs           3.9G     0  3.9G   0% /proc/acpi
tmpfs           3.9G     0  3.9G   0% /proc/scsi
tmpfs           3.9G     0  3.9G   0% /sys/firmware

    13/04/2021

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From pet to cattle
Treat your kubernetes clusters like cattle, not pets